Yeah that’s the downside. But also, it’s been almost 20 years since the original. Technology has changed a ton. It does suck that a lot of the old mods won’t be updated, but it brings in opportunity for new mods.

Nothing is going to stop you from playing the originals with mods though.

Highly doubt any of the original mods would work with the remastered ones though, if they use a different engine. The Oblivion remaster used Unreal Engine 5 to handle all of the visuals, but kept Gamebryo as the base engine for all of the underlying mechanics. Virtually none of the existing mods for the original Oblivion worked with the remaster, but new ones could be created.

I would expect the same thing to happen with FO3 and FNV remasters.